Geologic formations are used for many purposes such as hydrocarbon production, geothermal production and carbon dioxide sequestration. Boreholes are typically drilled into the earth in order to intersect and access the formations.
Acoustic borehole logging instruments are used to estimate parameters of interest of the formation. For example, these downhole tools may measure velocities of earth formations in one or more modes of acoustic energy propagation. Acoustic borehole logging instruments are typically used in liquid-filled boreholes drilled through the earth formations. Velocity is generally determined using these instruments by measuring the time taken by an acoustic energy pulse to traverse a particular distance along the wall of the wellbore. Conventional acoustic logging methods can also measure sound speed and attenuation at a fundamental-mode frequency to estimate parameters of interest (e.g., formation properties).
Hydraulic fracturing and other stimulation techniques may be applied to the formation to facilitate removal of hydrocarbons by fracturing the formation and/or extending existing fractures in the formation. Evaluation of the extent, complexity, and orientation of fractures is relevant to evaluating hydraulic fracturing operations, monitoring the fracture system, and managing operations in the formation.
The estimation of mechanical parameters of an earth formation may also be determined via various downhole operations or by analysis of a sample volume of the formation brought to the surface. These mechanical parameters may be important for many applications such as reservoir stress-state determination, horizontal drilling and hydraulic fracturing design. These parameters include Young's modulus, Poisson's ratio, cohesion, angle of internal friction, Mohr-Coulomb failure envelope, and unconfined compressive strength. Their determination is commonly performed via core sample analysis, including compression tests of core samples at various confining pressures. Characterizing these parameters facilitates optimization of further operations conducted in the formation, such as fracturing operations, drilling, or other exploration or completion operations of a typical oil or gas well.